Quote:
Originally Posted by Toobuilder
but the crank was packed full of sludge
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I also noticed mine was full of sludge when I went looking to see if I could do a constant speed conversion. I was concerned about having the dregs move backwards and fall in the crankcase, but turned out it wasn't a big deal. I used an old hacksaw blade, plus a narrow nozzle on a shop vac. Broke it loose with the blade, then vacuumed it out.
I thought I was done, but just now noticed a Lycoming service bulletin on cleaning and checking this area, 505B. Much detail here about what to check for. Purely optional for non-commercial flyers, but a good to-do list if you find corrosion. I think I'll go back for a second look, might as well, it is still apart.
This area of the crank reminds me of a bowl centrifuge, a device that works wonderfully at isolating particles that might take weeks to separate at only 1 G. I'd be very surprised if this wasn't the intent of a couple smart old Lycoming engineers. It has a high G environment, almost 200 g's at 2700 rpm, a pond area offering retention time for the oil (widest diameter), a dam (narrowed diameter) is the exit area back into the crankcase for the clarified oil. Only thing that isn't real obvious, how does the fixed pitch engine feed this tiny oil clarifier? Is it the front main bearing or splash though the end? Seems like whether fixed or constant speed, the solids are retained in the pond and removed either at rebuild or when inspecting. Removing the solids seems like a good thing to do once in a while, since once the "pond" fills with sludge, you've got no retention time nor anywhere for the solids to sit, so they are going right back into the crankcase. Once again very impressed by this decades old engine design.